test/dashboard: fix segfault when importing dm.xmlsec.binding

test/dashboard: fix segfault when importing dm.xmlsec.binding

python-saml depends on dm.xmlsec.binding which is a python binding of
xmlsec C library. but without -DXMLSEC_NO_SIZE_T the compiled
dm.xmlsec.binding segfaults when `import dm.xmlsec.binding`. see
https://github.com/onelogin/python-saml/issues/30 and
https://github.com/4teamwork/ftw.saml2auth/issues/3 .

in long term, we might want to switch to python-saml, see
http://tracker.ceph.com/issues/37081

Signed-off-by: Kefu Chai <kchai@redhat.com>